Communicate with N64 Controller using Raspberry Pi Pico with MicroPython

main.py

from rp2 import PIO, StateMachine, asm_pio
from machine import Pin
import time

dataPin = Pin(0)  # GP0


@asm_pio(out_init=PIO.OUT_HIGH, set_init=PIO.OUT_HIGH, sideset_init=PIO.OUT_HIGH,
         out_shiftdir=PIO.SHIFT_LEFT, pull_thresh=32, autopull=False,
         in_shiftdir=PIO.SHIFT_LEFT, push_thresh=32, autopush=False)
def joybus_write_read():
    # prepare for detect Controller Stop Bit
    set(y, 0b1111)

    # write data ------------------------
    set(pindirs, 1).side(1)          # 1:output

    # 4 cycles loop
    wrap_target()
    pull(ifempty)
    # to send Console Stop Bit, put 0xffffffff to osr
    # normally osr has at least one 0 bit, so put(0xffffffff) to osr explicitly to stop
    mov(x, invert(osr))
    jmp(not_x, "send_stopbit")

    out(pins, 1)            # shift out from OSR
    wrap()

    # ------------------------
    label("send_stopbit")
    set(pins, 0)[3]          # Console Stop Bit (1us LOW/>2us HIGH)
    set(pindirs, 0)          # 0:input

    # if no controller connected, pin goes LOW here

    # wait for falling edge
    wait(0, pin, 0)

    # ------------------------
    # 4 cycles loop
    label("readloop")
    in_(pins, 1)     # shift in
    push(iffull)
    # check Controller Stop Bit (2us LOW/>2us HIGH)
    mov(x, isr)
    jmp(x_not_y, "readloop")

    label("end")
    jmp("end")


def get_byte(in_bits):
    # convert from lower 4 bits
    # ex) 0001 0001 0001 0001 0001 0111 0001 0111
    #      (0)  (0)  (0)  (0)  (0)  (1)  (0)  (1)
    # -> 0x05 = 0b00000101
    ib = in_bits
    r = 0
    for i in range(8):
        r = r >> 1
        if (ib & 0x0000000f) == 0b0111:  # One
            r = r | 0b10000000
        ib = ib >> 4
    print(f'>> {r:02x}: {in_bits:032b}')
    return r


def get_bits(out_byte):
    # convert from LSB
    # ex) 0x12 = 0b00010010
    # -> 0001 0001 0001 0111 0001 0001 0111 0001
    ob = out_byte
    r = 0
    for i in range(8):
        r = r << 4
        if (ob & 0x80) == 0x80:
            r = r | 0b0111  # One
        else:
            r = r | 0b0001  # Zero
        ob = ob << 1
    print(f'<< {out_byte:02x}: {r:032b}')
    return r


def send_bits(sm, bits):
    array = []
    for a in bits:
        array.append(get_bits(a))
    array.append(0xffffffff)  # Stop
    for b in array:
        sm.put(b)


def recv_bits(sm):
    while sm.rx_fifo() > 0:
        v = sm.get()
        get_byte(v)


# 4MHz (0.25us/cycle)
sm = StateMachine(0, joybus_write_read, freq=4000000, set_base=dataPin,
                  sideset_base=dataPin, out_base=dataPin, in_base=dataPin)
sm.active(1)


while True:
    print("send")
    send_bits(sm, [0x01])

    print("recv")
    recv_bits(sm)

    time.sleep_ms(100)
    sm.restart()